My goal is to live in a monkey hut that resembles an ohmu from Nausicaa. For that, it needs 14 eyes that glow either red or blue, depending on my hut's mood. I was thinking of using those cheap LED flashlights with like a dozen LEDs arranged inside a mirror dome, putting coloured filters on them, and running them on two separate circuits that I can toggle with a switch from the inside.

But, I'm no electrician, have never wired anything before, and have never build anything revolving around LED lighting. The things I don't know could fill the internet. Can anyone with some expertise in the matter give me some pointers and ballpark figures to work with?

1. I know LEDs use very little power, but I'm going to need to run a lot of them at once (168, most likely), all night long, every night. Any ideas what kind of battery stock I need to have on hand to sustain this big array of lights that I'm planning?

2. All that stuff about voltage, current, and resistance that they teach you in high school? I remember the equations, but I have no numbers from the real world to plug into them. Does anyone have an estimate of how many LED lamps I can string in parallel before frying the wire, how many I can put in series before I need to up the voltage? And do I need to add in any resistors (I'm thinking off the shelf flashlight lamps, so I don't foresee needing resistors, but... I don't know).

3. What's the best practice for protecting my wiring from rain and careless splashes of vodka drinks?

4. What about other technologies, like CFLs? Are they worth pursuing?

5. I also want to wire up a small solar panel or light sensor so that the lights automatically turn on a dusk and turn off at dawn. Has anybody done that sort of thing before? How do you wire it up, and how expensive are the panels/sensors? And how easily are they tricked by other light sources (moon light, flashlights, flame bursts, etc) and by clouds blocking the sunlight?

168 LEDs is nothing, really. You could run them all off of a 4 - AA battery pack which would give you a 6v source. Put that in your calculations. White LEDs usually need about 3.2v of forward voltage, and you'll want to run them at 15-20mA. 22AWG stranded hookup wire would be fine as you're really not pulling all that much current depending on how far your wiring is going. Even then.. 168 LEDs really isn't all that much.

You could take the time to figure all this out, use the LED wizard, get resistors, make your own LED clusters.. which.. really is not all that hard... or.. you could get rope light and cluster up a few lights.. add extension wires inbetween the clusters.. and voila.

Don't use filters, use LEDs for your specific color. Filters will never net you the same quality of color, nor the brightness.

I'm not so sure 168 LEDs is "nothing". 168 LEDs runing at about 20mA each (pretty standard), is about 3.4 amps of current. A D cell battery has about 22 Amp * hours (AH) of capacity, so you'd be able to run those 168 LEDs about 6 hours straight before a battery change. Not bad, but you will need to do battery changes, maybe even twice per night; for sufficient voltage you'll need multiple D-cells.

There are also 220AH deep cycle batteries you can buy, and would probably last you the entire burn, but at $80 each that may not be in your best interest (you should only discharge to 50%, so effectively 110AH of use). They may cost you more than the one-off cost of $1.10 per D-cell, three (3) D-cells per 6 hours, and 1-2 sets per night. Plus you'd need to buy a smart charger for them if you want to reuse them (which you should!).

I'm not sure how the ohmu is supposed to animate, but something you could try is to make the eyes pulsate in brightness like the machines in the Animatrix 2nd Renaissance ending (example) . You can rig that up with Arduinos or 555 timer circuits, or something on that order for pretty cheap. The fact that it will not be on all the time will also reduce the power requirements.

Here's a circuit that you can use to shut off the LED when there is light outside.

"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

BBadger wrote:I'm not so sure 168 LEDs is "nothing". 168 LEDs runing at about 20mA each (pretty standard), is about 3.4 amps of current.

You're assuming that he's paralleling all 168 LEDs at straight 3v.. which would be silly.. as you would be much better off making little mini-series clusters and running at higher voltage.. at least 12v.

BBadger wrote:I'm not so sure 168 LEDs is "nothing". 168 LEDs runing at about 20mA each (pretty standard), is about 3.4 amps of current.

You're assuming that he's paralleling all 168 LEDs at straight 3v.. which would be silly.. as you would be much better off making little mini-series clusters and running at higher voltage.. at least 12v.

Higher V.. lower draw.

junglesmacks, I'm not even concerned with the topology with this calculation. Don't jump over every current calculation thinking that saving current is the same thing as saving power. I'm calculating how many batteries he's going to need to power this rig. 12V? 3V? Who cares? The LEDs will each be using 3V at 20mA each, no matter if you put them in series or in parallel. To get 12V you'd need 8 D-cell batteries in series using (168 / 4) * 20mA = 0.84A, with 22AH of juice. With the same 8 batteries I could power the LEDs at 3V at 3.36A but with 88AH of juice. Using a (perfect) boost circuit I could even power the same set at 1.5V drawing 6.72A with 176AH of juice (better check that discharge rate on the battery and the wiring thickness). Guess what? It'll all run the same length of time on the same number of batteries! Power = Current * Voltage remember?

If you want to discuss topologies, that's that's a different matter. Even then, there's no clear-cut solution. I realize that the series-LEDs-current-limiting-resistor topology worked awesome for your suit this year, but it is not the end-all and be-all LED circuit, and not all designs can be built around its ideals. I remember on my own lit-up costume this year I had to power my hat with 6x AA batteries. It sucked having to string that damn thing to my shirt pocket. I would've rather have had a smaller number of batteries that I could change out less frequently, and have left in the hat itself. A single D-cell in a boost circuit would've been nice. Likewise, it may suck having to string together 8x batteries just to power up something portable because it needs 12V of power. The EL wire on my bike used a mere 2AA batteries which was much better than 6x in my hat. Trade-offs.

In Ohmu's case, portability is probably not the major limiting factor. The project should probably design the clusters around the number of eyes that Ohmu thing has and the brightness it needs, not around some fixed voltage number. There are other factors as well, such as control resolution; what you gain in longer chains of LEDs you lose in control resolution. Furthermore, it may not even be in his best interest to use high-voltage, resistor-based limiting circuits, or even multiple LEDs to achieve the effect he needs. Single large, high-current LEDs may be easier to work with than long chains of low-current LEDs, and he can employ better powering circuits such as bucking topologies that can cut down on power usage. In the end though, the power usage remains the same.

"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

Ok.. back to the OP. Bbadg.. remember that while this stuff makes sense to you and I, we're gonna lose the OP if we/you/i/anyone doesn't give him simplified explanations. I'll take the time later to answer.. but right now, the girl is in her bathing suit ready to go on that boat and I'm about to oblige. Sunday Funday here we come..

ohmu wrote:I work with a bunch of electrical engineers (I'm a software guy myself). I can probably figure this out, but I'm too hung over right now to read any of it.

But you mentioned using a charger to reuse my batteries. That means I need to borrow the use of someone's generator, doesn't it?

It depends on if you're near to the generator. Those deep cycle batteries are heavy, so you probably wouldn't want to be hauling them around much to charge. Make sure you buy a smart charger so that you get the most out of your deep cycle batteries. The smart charger adjusts the charging rate in different phases to ensure that your battery maintains a long life. You may even consider using solar energy out there in the playa to help charge the batteries, and you can use it for other things besides just those batteries.

"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

So in summary, what voltage do you suggest I go with? 3V? 6V? 12V? What does each LED require, and what would I require if I had, say, clusters of a dozen LEDs in parallel, and 14 clusters in series? Or vice versa?

You mentioned using coloured LEDs instead of filtering white ones. I agree on principle, but it seems difficult to find coloured LED lamps off the shelf - at my local electronics store I can only find them sold individually at ridiculous markups. I've never soldered anything, and don't really want to open that can of worms - a coworker mentioned using clamps to draw heat to avoid frying the LED, and I ask myself, "what else do I not know that I should?". Any favourite sites where I can order pre-made lamps of whatever colour I want?

Hmm, well first things first, do you want to control each "eye" separately? If so, you could just make a relatively simple LED cluster for each eye powered by a few AAs. You could easily build them on perfboard and have two switches, one for on/off and one for red/blue. Just buy the LEDs in bulk online (5mm LEDs are pretty cheap, no matter the color)

Now, that ALL being said, if you don't want to dive into the electronics side of this to build something custom, FIGJAMs idea of using solar LED strings would work just fine. You'd just have to get two per eye and color one blue and one red. Figuring out how to externally mount the solar panels might be a challenge though.

The lights will be external, but under glass or plastic domes. I can probably just plop the solar panel next to them, just outside the surrounding tarp or whatever more rigid material on which they rest.

Each eye need not be independent. I was planning to do a single circuit for all 14 blue clusters, and another circuit for all 14 red clusters. I'll probably just bring a whole whack of D-cells, forget charging them (I don't like plans that rely on the kindness of strangers - strangers are often kind, but only when you don't expect anything out of them). Unless maybe one of those 6V lantern batteries would give me better efficiency?

All depends on how bright and/or spectacular you want this to be. A couple of led rope light strings will get you under $50-$70.. as will doing it yourself. I think a bigger consideration is how much time you want to invest in this. The actual LEDs these days are dirt cheap.. I just ordered another batch for about $0.03/each. It's the time spent wiring and figuring that will get you. All for the love though.. and careful, you may find yourself with yet another obsession..

Mostly just seeing what you'd be willing to spend per-eye. You could get some of those 1W LEDs on stars for less than a buck each, and then attach them to these constant current drivers (even chain a few up with higher input voltages). The drivers are really cheap if you apply that bulk rate discount. Then all you do is apply power to whichever set you wish to have on.

"The essence of tyranny is not iron law. It is capricious law." -- Christopher Hitchens

That idea sounds like a winner! You would want the "eyes" to be a diffused, semi-translucent white though preferably in order to illuminate them fully and not so concentrated right where the light is. Find a way to mount them at least a few inches back and suspended right in the middle, too.

Are 168 LED lights really needed for this application? If the eyes just need to glow this could be done with 2-3 red and blue high output LEDs per eye I would think. Are you wanting to illuminate the area around the hut, or just make the hut look cool?

You don't have to use a clip when soldering an LED. All semiconductors are sensitive to overheating when being soldered, but I have yet to fry an unprotected LED. There are a zillion professional best practices that you can get into, or you can just watch a few youtube videos, have fun and start soldering - I think that you will be happy that you opened that can of worms.

You can apparently use sandpaper to diffuse an LED - I am about to try this out as the high output LEDs have a very narrow viewing angle, but put out a painful amount of light.

I think that you could use 2 PWM dimmers, one for red and one for blue, if you just want to manually dial in and fade the shade and intensity of the light. It also seems like it could be a good simple arduino project. The "analog" outputs of the arduino are really PWM outs, so you could run a BJT or MOSFET from those and power the red and blue channels in each eye.

Again, unless you really want to throw a lot of light around, this project would be a lot easier and lower power if you just had 20 mA blue and 20 mA red in each eye maximum. The whole hut would be 560 mA peak, and likely only 100-200 mA with normal operation. This you can run on something simple like lantern batteries or rechargeable AAs.